Many modern wireless communication devices (e.g., cell phones, PDAs, etc.) utilize transceivers having both a transmitter section (i.e., transmission chain) configured to transmit data and a receiver section (i.e., receiver chain) configured to receive data over radio frequencies.
For example, FIG. 1a illustrates a wireless communication transceiver 100 comprising a transmitter section 102 and a receiver section 104. In order to reduce the hardware used by transceiver 100, a duplexer 106 may be configured to couple both transmitter section 102 and receiver section 104 to a common antenna 108. To achieve high data rates, transceiver 100 may be configured to operate in full-duplex mode, wherein both transmitter section 102 and receiver section 104 use antenna 108 at the same time. During full-duplex mode operation, transmitter section 102 typically uses one carrier frequency while receiver section 104 uses another carrier frequency.
Despite using different frequencies, intermodulation distortion may arise during operation of transceiver 100. Intermodulation distortion occurs when a modulated blocker passes a component with a nonlinear characteristic, forming a spurious signal (e.g., an additional signal at a frequency that are not at harmonic frequencies of a received signal, but are instead at a sum and difference of the original signal frequency) in a reception path that interferes with a received differential input signal.
Second-order intermodulation distortion is caused by multiplication of two interferer signals. FIG. 1b illustrates a frequency graph 110 showing an RF second-order intermodulation distortion (i.e., second order intermodulation distortion at RF frequencies) generated by interferer signals. As illustrated in graph 110, the frequency domain comprises a plurality of interferer signals at frequencies f1, f2, and f3. Although the frequencies of the interferer signals are not close to a received differential input signal frequency fR, the interferer signals may combine together to form spurious signals, 112 and 114, comprising products having a sum or difference of their frequencies (e.g., f1+f2, f3−f2). Spurious signals that land at an RF frequency occupied by received differential input signal frequency fR cause second-order intermodulation distortion that is detrimental to operation of the transceiver system. Once intermodulation distortion appears within the reception path, there is no way of distinguishing it from the desired signal and transceiver sensitivity is degraded.